Randomized Bit Encoding for Stronger Backward Channel Protection in RFID Systems

Abstract

In this paper, we introduce a randomized bit encoding scheme that can strengthen the privacy protection on RFID tags. This scheme is used together with the backward channel protection method proposed by Choi and Roh in [1], which serves to protect the unique identifier of an RFID tag from disclosure to close-range eavesdroppers. Choi and Roh's method faces the 'same-bit' problem, in which some bits of the unique identifier could be disclosed, thereby revealing critical information. Our proposed scheme alleviates the 'same-bit' problem to a negligible level. Furthermore, we propose an enhanced system model that can protect the unique tag identifier from disclosure not only against eavesdroppers, but against unauthorized interrogators as well. A metric based on entropy was defined and used to measure the amount of protection offered by the scheme. A method to construct an optimal randomized n-bit encoding scheme was also described. In addition, theoretical analysis and simulations were conducted, which show that the proposed encoding scheme provides significant improvement (achieving almost twice the entropy) over no encoding.

Dynamic Bit Encoding for Privacy Protection against Correlation Attacks in RFID Backward Channel

“…Lim et al [18] introduce a randomized bit encoding scheme (RBE) which is able to alleviate the same bit problem of the technique in [3]. In RBE, each bit of a real tag ID is encoded into an n-bit string and a tag sends its encoded ID to a reader under the privacy masking protocol.…”

“…In this paper, we adopt the architecture in [18] and assume the deployment of TMDs. In addition, we assume that each tag takes part in the singulation process with a randomly generated pseudo ID.…”

“…For the randomized bit encoding (RBE) scheme [18], the probability that all bits in a codeword do not collide with the mask bit string is 1 2 n with the optimal n-bit encoding. The probability that a bit is identifiable is…”

“…Nevertheless, this method suffers from the same bit problem, in which some bits of the tag ID could still be disclosed. An improved solution based on [3] is presented in [18] by encoding each source bit of the tag into a fixed length n-bit string to alleviate the same bit problem. This solution is still vulnerable if an attacker has knowledge of the n-bit string length and can interrogate a tag repeatedly (detailed in the Motivations subsection of Section 3).…”

“…• Analytical models of guessing attacks [18], anonymity against generated encoded ID and correlation attacks are created and validated.…”